The present invention relates to a low-water-consumption method for processing an exposed color reversal photographic film. Conventionally, the processing of a color reversal material comprises first a black and white development step, a first washing step, a reversal step, and a color development step.
In the conventional processing of color reversal films, the reversal step between the black and white development step and the color development step is conducted either chemically (by a chemical agent) or by fogging. In the reversal step, the silver halides not initially exposed are rendered developable. Such a processing method of color reversal films is well known and described in detail in xe2x80x9cChimie et Physique Photographiquesxe2x80x9d, Volume 2, P Glafkides, 5th edition, Chapter XL, pages 947-967.
One example of such a color reversal processing is the Ektachrome E-6(copyright) processing described on page 954 of the above mentioned handbook. During the Ektachrome E-6(copyright) photographic processing, the photographic material is successively circulated through each of the following baths:
a) a black and white development bath,
b) a first washing bath, c) a chemical reversal bath,
d) a color development bath, e) a conditioning bath,
f) a bleaching bath,
g) a fixing bath,
h) one or more washing baths, and
i) a rinsing bath.
Then, one proceeds to a drying step.
In general, it is desired that photographic materials be developed automatically and as fast as possible. Now during the circulation of the photographic material from bath to bath, chemical components are carried from one bath to another either by means of the photographic material, or by the conveyor belts of the photographic processor. These chemical components accumulate in the processing baths whose efficiency they reduce. The carry-over of these chemical components gets more significant as the processing of the photographic materials gets faster.
In order to minimize the contamination of the baths by these chemical components, a replenishment solution can be used. In particular, for the reversal bath, the replenishment solution is introduced in the spent bath to be replenished, and an equivalent volume of the spent bath is rejected via the overflow. A spent bath is a bath that is no longer usable photographically. This method generates a significant volume of spent baths, thus a significant volume of effluents.
Another method to minimize the carry-over of chemical components consists in replenishing the washing baths by the continuous addition of clean water in order to maintain a very low concentration of chemical products in these washing baths. This is the reason why a first washing bath is placed between the first black and white development bath and the chemical reversal bath. This first washing bath interrupts the chemical reactions caused by the components of the first development bath, prevent the migration by carry-over from the first developer into the reversal bath and thus prevent deterioration of the quality of the image of the developed film. In Ektachrome E-6(copyright) standard processing, it is usual, for washing baths, to use a continuous water supply that can reach a flow rate of 7.5 liters per minute. Such a method results in considerable water consumption, which increases the cost of the processing. In addition, processing laboratories must now satisfy certain regulations that very clearly restrict water consumption per square meter of developed films. However, when the water supply to the first washing bath is reduced, a rise of this bath""s pH and a deterioration of the sensitometry of the developed films are observed.
The present invention provides a method for processing color reversal photographic film that enables significant reduction of the water consumption of the first washing bath situated between the black and white development bath and the chemical reversal bath, while keeping the pH of this first washing bath between 5 and 7, and without deterioration of the sensitometric characteristics of developed films. The invention further provides a photographic processing method that reduces the volume of the spent solution leaving the reversal bath.
The method of the invention for processing an exposed color reversal photographic film comprises the steps of circulating the exposed film in:
i) a black and white development bath,
ii) a first washing bath,
iii) a chemical reversal bath comprising at least a buffer agent capable to pass through a nanofiltration membrane,
this method comprising further the steps of collecting the waters leaving the reversal bath (by overflow and/or by draining), circulating the collected waters through a nanofiltration unit to produce a permeate, recycling the permeate in the first washing bath and rejecting via an overflow a water volume at least equivalent to that supplied by the permeate, the buffer agent being chosen so as to keep the pH in the first washing bath between 5 and 7.